By way of example, Japanese Laid-Open Patent Application No. 138,043/1981 discloses a system for controlling the projection angle of a vehicle headlamp. In this system, the optical axis of a retractable headlight is controlled automatically by a switch mounted on a shock absorber and which is turned on and off in response to a pressure of a given magnitude. The switch is turned on whenever a mean pressure of the shock absorber exceeds a given value. The mean pressure depends on the elevation of the vehicle or on the inclination of the car body if the switch is mounted on a shock absorber associated with rear wheels. A headlamp is supported by an electric drive mechanism which includes a first brush contact UP for driving the lamp upward, a second brush contact DW for driving it downward, and a third brush contact FM which stops the tilting movement of the lamp at a position which is located slightly below the up position. The projection angle of the lamp can be varied by adjusting the length of the brush contact EM. The switch mentioned above activates a relay driver when it is turned on, thereby controlling the optical axis. It will be seen that the choice of the projection angle is limited to a single value.
French Patent Specification No. 1,592,664 discloses a system including four switches which detect the elevation of the vehicle in several different zones so as to permit the projection angle of the headlamp to be controlled among several values.
It may be concluded that an arrangement of either cited reference represents a lamp drive and control apparatus which includes a lamp angle detector means and a lamp angle command means so that the inclination or the position of the lamp may be controlled in accordance with the status of such means. A brush and a sensor switch mounted on a headlamp tilting mechanism may be selectively connected to energize an electric motor for forward or reverse rotation or to stop it, thus automatically establishing a projection angle of the lamp.
In a retractable headlamp system in which a headlamp may be moved between a stowed position and an extended position, it is preferred that a lamp drive mechanism be provided with a single electric motor which may be used to drive the headlamp between the stowed and the extended position in one instance and to provide a fine adjustment of the angle of the optical axis or the projection angle of the headlamp in its extended position in accordance with the elevation or inclination of the vehicle.
However, when a single motor is used in common, there arises a problem. Specifically, to achieve a retracting movement having an increased stroke, it is desirable that the lamp be rapidly driven from its stowed to its extended position or reversely, thus requiring an increased torque to drive the motor. Conversely, when controlling the projection angle in the extended position of the lamp, the extent of angle control is limited while a higher precision is required. The drive need not be effected at a high rate, and rather it is preferred to drive the motor at a low rate to achieve the required control accuracy while preventing the occurrence of an overrun, for example. Thus a conflict exists between the requirements for the energization of the motor for retracting movement and for the control of the projection angle.
It may appear that such conflicting requirements can be satisfied simultaneously by employing two different values of voltage or current for energizing the motor so that an increased voltage or current may be applied to the motor to develop an increased torque for the retracting movement while a reduced voltage or current may be applied to the motor to develop a low torque for the control of the projection angle. However, there still exists a problem in that in the event of a jamming of a headlamp drive mechanism or an increased load at low temperatures, the low torque developed by the motor may not be sufficient to drive the mechanism effectively, resulting in a locked condition which fails to achieve the desired function.
At any rate, it will be seen that a conventional headlamp drive and control apparatus includes lamp angle detector means and lamp angle command means so that the inclination or position of the headlamp may be controlled in accordance with the status of the both means.